Eta (uppercase/lowercase Η η) is a letter of the Greek alphabet.
In very early Greek writing it stood for the consonant sound "h", but in Classical Greek it stood for a long vowel "e". In Modern Greek, it is pronounced as "i". In the system of Greek numerals, it has a value of 8. Letters that came from it include the Roman H and Cyrillic И.
In mathematics, the lowercase η is used to represent Dirichlet eta function. The same letter is also used to represent conformal time in cosmology, efficiency in telecommunications and elasticity in economics.
This article uses material from the Wikipedia Simple English article Eta, which is released under the Creative Commons Attribution-ShareAlike 3.0 license ("CC BY-SA 3.0"); additional terms may apply (view authors). Content is available under CC BY-SA 4.0 unless otherwise noted. Images, videos and audio are available under their respective licenses.
®Wikipedia is a registered trademark of the Wiki Foundation, Inc. Wiki Simple English (DUHOCTRUNGQUOC.VN) is an independent company and has no affiliation with Wiki Foundation.